Error parsing XML: not well-formed (invalid token) error, no cause

            
android: id = "@ + id / factorOne"

android: layout_width = "fill_parent"
android: layout_height = "wrap_content"
android: text = "@ string / hello_world"
/>

android: id = "@ + id / operation"
android: layout_width = "wrap_content"
android: layout_height = "wrap_content"
android: text = "@ string / hello_world"
/>

android: id = "@ + id / factorTwo"
android: layout_width = "fill_parent"
android: layout_height = "wrap_content"
android: text = "@ string / hello_world"
/>